Cooling systems, as found e.g. in HVAC equipment, typically employ vapor-compression technology. Many of the refrigerants historically used in such systems are environmentally problematic. Alternative systems for cooling that do not rely on vapor-compression include evaporative chillers and membrane heat pumps.
Evaporative chillers use liquid water to absorb sensible heat from a fluid source, usually outside air, by evaporating the water to cool the air. But they are limited as a practical matter to environments where the outside air is dry and hot; and their efficacy decreases with increasing air humidity; moreover, their dehumidification abilities are limited and they often entail high water usage.
Membrane heat pumps provide sensible and latent cooling by utilizing selectively permeable membranes that enable both water molecules and the thermal energy that is related to evaporation to move. Current systems, however, are large and complex, and employ separate equipment and process stages, including multiple membranes, for the latent and sensible cooling functions. The systems typically also require a large expirator and vapor pump(s), and do not provide for recapturing and reusing waste heat from other processes.
There is thus a need for improved membrane heat pumps that are scalable, simplified and compact, energy-efficient, and have enhanced performance efficiency through thermal activation.
In one non-limiting aspect thereof, exemplary embodiments of the invention provide a membrane-based assembly comprising a vapor-removing element comprising, at least one flow volume region adapted to receive a working fluid flow under partial vacuum, the at least one flow volume region having a first surface in mass transfer relationship with a first side of a first selectively permeable membrane, the first selectively permeable membrane having a second side configured for contact with a vapor-containing gas to permit transfer of at least a portion of the vapor from the vapor-containing gas through the selectively vapor-permeable membrane and into the working fluid flow.
In yet another non-limiting aspect thereof, exemplary embodiments of the invention provide a membrane-based assembly comprising a cooling element, wherein the cooling element comprises a mass transfer relationship between the working fluid flow and an evaporable liquid to permit formation of an evaporant from the evaporable liquid and transfer of at least a portion of the evaporant from the liquid into the working fluid flow.
In non-limiting aspects thereof, the mass transfer relationship between the working fluid flow and an evaporable liquid comprises a second selectively-permeable membrane. In still other non-limiting aspects thereof, the mass transfer relationship between the working fluid flow and an evaporable liquid does not require a second selectively-permeable membrane.
In yet another non-limiting aspect thereof, a membrane-based assembly comprises a combination of the cooling and vapor-removing elements in a single, integrated unit.
In yet another non-limiting aspect thereof, embodiments provide an apparatus comprising a plurality of vapor-removing assemblies, cooling assemblies, and/or combinations thereof disposed in a stacked arrangement.
In yet another non-limiting aspect thereof, a system is provided comprising a dehumidifying and/or cooling apparatus; a vacuum pump to initiate the partial vacuum within the working fluid; and an expirator for maintaining the system under partial vacuum. In non-limiting aspects thereof, the membrane-based expirator comprises at least one third selectively permeable membrane having a first side in mass transfer relationship with the working fluid and; a fluid displacement device, wherein said fluid displacement device creates conditions sufficient to permit the water vapor contained with the working fluid to transfer from the working fluid through the third selectively permeable membrane to a second side of the third membrane. In yet another non-limiting aspect thereof, the expirator is thermally activated using thermal energy from a waste heat source.
In yet another non-limiting aspect thereof, exemplary embodiments of the invention provide that the selectively permeable membranes comprise a microporous PTFE membrane, a perfluorosufonate ionomer membrane, a PTFE/PAO/PU membrane, a PTFE/PAO/PU laminate, a polyester/polyether membrane, a polyester/polyether laminate, a derivatized cellophane membrane, a chemical protective laminate, flashspun high-density polyethylene fiber paper, flashspun high-density polyethylene fiber paper impregnated with a vapor permeable polymer, polyethersulfone, sulfonated poly(ether ether ketone), or combinations thereof.
In yet another non-limiting aspect thereof, exemplary embodiments of the invention provide a process for removing vapor from a vapor-containing gas and/or cooling an evaporable liquid.